(a) Field of the Invention
This invention relates to pyrazolo[3,4-b]pyridin-3-amines, their preparation and their use as cardiotonics.
(b) Description of the Prior Art
Chemical Abstracts Vol. 87, item 39,357t, 1977, reads as follows:
"Dipyridyls. VII. Reaction of .beta.-ketoaldehydes with cyanoacetic acid hydrazide. Balicki, Roman; Kaczmarek, Lukasz; Nantka-Namirski, Pawel (Inst. Org. Chem., Pol. Acad. Sci., Warsaw, Pol.). Acta Pol. Pharm. 1976, 33(3), 289-93 (Pol). RCOCH.sub.2 CHO (R=Me, Ph, 3- and 4-pyridyl, and ##STR1## 6-methyl-3-pyridyl) condensed in an alk. medium with NCCH.sub.2 CONHNH.sub.2 (I) to give the pyrazolpyridines II. II were also obtained when 5-amino-3-pyrazolone was used instead of I. II (R=3- and 4-pyridyl) were also prepd. in the reaction of Me 6-(3- and 4-pyridyl)-2-chloronicotinates or 6-(3- and 4-pyridyl)-2-chloro-3-cyanopyridines with 80% Nh.sub.2 Nh.sub.2.H.sub.2 O."
The original article (p. 291) shows that the compounds of formula II (supra) can also exist in tautomeric 1,2-dihydro-6-R-2H-pyrazolo[3,4-b]pyridin-3-one form.
In a later paper entitled "Cancerostatics III. Synthesis and Some Chemical Transformations of 3-Cyano-5-(pyridyl-4)pyrid-2-one" [Pol. J. Pharmacol. Pharm. 30, 707-712 (1978)], P. Nantka-Namorski and L. Kaczmarek show, inter alia, the reaction of 3-cyano-5-(4-pyridinyl)pyridin-2-one [alternatively named 1,2-dihydro-2-oxo-5-(4-pyrridinyl)nicotinitrile] with phosphorus oxychloride to prepare 2-chloro-3-cyano-5-(4-pyridinyl)pyridine [alternatively named 2-chloro-5-(4-pyridinyl)nicotinonitrile].